Application of sequence hopping and orthogonal covering codes to uplink reference signals

ABSTRACT

Methods and apparatuses are provided for transmitting and receiving references signals. A method includes receiving a first parameter, which is a cell specific parameter; receiving a second parameter, which is a UE specific parameter; receiving a cyclic shift indicator (CSI) indicating a cyclic shift for a sequence and an orthogonal covering code; acquiring the reference signal for a physical uplink shared channel (PUSCH), based on the CSI and the second parameter; and transmitting the reference signal on the PUSCH. Group sequence hopping is not applied to acquire the reference signal, if the first parameter indicates that the group sequence hopping is enabled and the second parameter indicates that the group sequence hopping is disabled. The first parameter includes a group hopping enabled parameter, and the group sequence hopping includes hopping among different groups.

PRIORITY

The present application is a Continuation of U.S. application Ser. No.14/500,095, which was filed in the U.S. Patent and Trademark Office(USPTO) on Sep. 29, 2014, which is a Continuation of U.S. applicationSer. No. 13/920,754, which was filed in the USPTO on Jun. 18, 2013,issued as U.S. Pat. No. 8,848,761 on Sep. 30, 2014, which is aContinuation of U.S. application Ser. No. 13/032,257, which was filed inthe USPTO on Feb. 22, 2011, issued as U.S. Pat. No. 8,483,258 on Jul. 9,2013, and claims priority under 35 U.S.C. §119(e) to U.S. ProvisionalApplication No. 61/306,753, entitled “Applying Orthogonal Covering Codesto Uplink Reference Signals,” which was filed in the USPTO on Feb. 22,2010, the entire disclosure of each of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to wireless communicationsystems and, more particularly, to enhancing the functionality andenabling features of reference signals transmitted from a UserEquipment. The reference signals provide an estimate of the channelmedium experienced by the User Equipment at a given time instance.

2. Description of the Related Art

Several types of signals need to be supported for the properfunctionality of a communication system. In addition to data signals,conveying the information content, control signals also need to betransmitted from User Equipments (UEs) to their serving Base Station (BSor NodeB) in the UpLink (UL) of the communication system and from theserving NodeB to the UEs in the DownLink (DL) of the communicationsystem to enable proper processing of the data signals. For example,control signals include positive or negative ACKnowledgement signals(ACK or NACK, respectively) that are transmitted in response to (corrector incorrect, respectively) data packet reception and are associatedwith a Hybrid Automatic Repeat reQuest process (HARQ-ACK signals).Control signals also include Channel Quality Indication (CQI) signals,which a UE sends to the NodeB to provide information about the DLchannel conditions that the UE experiences. Further, Reference Signals(RS), also known as pilot signals, are typically transmitted to providechannel estimation and enable coherent demodulation for the transmitteddata or control signals or, in the UL, to be used by the receiving NodeBto measure the UL channel conditions the UE experiences. The former RSused for demodulation of data or control signals will be referred to asDeModulation RS (DMRS) while the latter RS, which are typically widebandin nature, are used for sounding the UL channel medium and will bereferred to as Sounding RS (SRS).

A UE, also commonly referred to as a terminal or a Mobile Station, maybe fixed or mobile and may be a wireless device, a cellular phone, apersonal computer device, and the like. A NodeB is generally a fixedstation and may also be referred to as a Base Transceiver System (BTS),an access point, or similar terminology.

UEs transmit data or control information through a Physical UplinkShared CHannel (PUSCH) while, in the absence of PUSCH transmission, theUEs transmit control information through a Physical Uplink ControlCHannel (PUCCH). A UE receives the signals conveying data informationthrough a Physical Downlink Shared CHannel (PDSCH) while signalsconveying control information are received through a Physical DownlinkControl CHannel (PDCCH).

A UE is assumed to transmit in the PUSCH or in the PUCCH over aTransmission Time Interval (TTI), which may, for example, correspond toa sub-frame with a duration of 1 millisecond (msec). FIG. 1 illustratesa block diagram of a sub-frame structure 110 for PUSCH transmission. Thesub-frame includes two slots. Each slot 120 includes seven symbols. Eachsymbol 130 further includes a Cyclic Prefix (CP) in order to mitigateinterference due to channel propagation effects. Some symbols in eachslot may be used for the DMRS transmission 140. The second DMRS in thesub-frame may or may not be transmitted with its negative value (scaledwith “−1”) 150 as it is subsequently described. The PUSCH transmissionBandWidth (BW) consists of frequency resource units, which will bereferred to as Resource Blocks (RBs). In one example, each RB includesN_(sc) ^(RB)=12 sub-carriers, which are also referred to as ResourceElements (REs). A UE may be allocated one or more RBs 160 for PUSCHtransmission and one RB for PUCCH transmission.

PUSCH transmission or PDSCH reception by a UE may be scheduled by theNodeB either dynamically, through a respective Scheduling Assignment(SA) conveying a Downlink Control Information (DCI) format in a PDCCH,or through Semi-Persistent Scheduling (SPS) using UE-specific higherlayer signaling such as Radio Resource Control (RRC) signaling. The DCIformat may inform a UE about a data packet transmission by the NodeB inthe PDSCH (DL SA) or about a data packet transmission to the NodeB (ULSA) in the PUSCH. With SPS, a UE transmits or receives data packets atpredetermined sub-frames.

FIG. 2 illustrates a processing chain at the NodeB for a SAtransmission. The Media Access Control (MAC) layer IDentity of the UE(UE ID) for which the SA is intended for masks the Cyclic RedundancyCheck (CRC) of the SA information bits in order to enable the UE toidentify that the SA is intended for it. The CRC 220 of the SAinformation bits 210 is computed and then masked 230 using the eXclusiveOR (XOR) operation between CRC bits and UE ID bits 240. An XOR operationonly evaluates to true where only one of the two input bits is 1. Thus,XOR(0,0)=0, XOR(0,1)=1, XOR(1,0)=1, XOR(1,1)=0. The masked CRC is thenappended to the SA information bits 250, channel coding (such asconvolutional coding) is performed 260, followed by rate matching 270 tothe allocated PDCCH resources, and finally by interleaving andmodulation 280, and transmission of the SA 290. It is assumed that boththe CRC and the UE ID have the same length such as, for example, 16bits.

The UE receiver performs the reverse operations of the NodeBtransmitter. This is illustrated in FIG. 3. The received control signal310 is demodulated and the resulting bits are de-interleaved 320, therate matching applied at the NodeB transmitter is restored 330 and thenfollowed by decoding 340. The SA bits 360 are then obtained afterextracting the CRC bits 350, which are then de-masked 370 by applyingthe XOR operation with the UE ID 380. Finally, the UE performs the CRCcheck 390. If the CRC check passes, the UE considers the SA as a validone and determines the parameters for signal reception (DL SA) or signaltransmission (UL SA). If the CRC check does not pass, the UE disregardsthe presumed SA.

The DMRS is assumed to be generated from Constant Amplitude ZeroAuto-Correlation (CAZAC) sequences. An example of such a sequence isgiven by the following Equation (1):

$\begin{matrix}{{c_{k}(n)} = {\exp\left\lbrack {\frac{{j2\pi}\; k}{L}\left( {n + {n\frac{n + 1}{2}}} \right)} \right\rbrack}} & {{Eq}.\mspace{14mu}(1)}\end{matrix}$where L is a length of the CAZAC sequence, n is an index of a sequenceelement, n={0, 1, 2, . . . , L−1}, and k is a sequence index. For CAZACsequences of length L, with L being a prime number, the number ofsequences is L−1. Therefore, an entire family of sequences is defined ask ranges in {1, 2, . . . , L−1}. However, the sequences for DMRStransmission need not be generated by strictly using the aboveexpression. As one RB is assumed to include N_(sc) ^(RB)=12 REs,CAZAC-based sequences can be generated either by truncating a longerprime length (such as length 13) CAZAC sequence or by extending ashorter prime length (such as length 11) CAZAC sequence by repeating itsfirst element(s) at the end (i.e., cyclic extension), although theresulting sequences do not strictly fulfill the definition of a CAZACsequence. Alternatively, CAZAC sequences can be generated through acomputer search for sequences satisfying the CAZAC properties.

FIG. 4 shows a DMRS transmitter structure at a UE based on a CAZACsequence. The frequency domain version of a CAZAC sequence may beobtained by applying a Discrete Fourier Transform (DFT) to its timedomain version. The frequency domain CAZAC-based sequence 410 isgenerated, the REs 420 in the assigned PUSCH transmission BW areselected 430, the Inverse Fast Fourier Transform (IFFT) is performed440, the Cyclic Shift (CS) 450 is applied, and, finally, the CP 460 andfiltering 470 are applied to the transmitted signal 480. The UE alsoapplies zero padding in REs where the DMRS is not transmitted, such asin REs used for signal transmission from another UE (not shown). ThePUSCH transmission BW may be contiguous, in accordance with the SC-FDMAtransmission principle, or non-contiguous in accordance with theDFT-Spread-OFDM (DFT-S-OFDM) transmission principle. For brevity,additional transmitter circuitry such as digital-to-analog converter,analog filters, amplifiers, and transmitter antennas, as they are knownin the art, are not shown.

The NodeB receiver performs the reverse functions of the UE transmitter.This is illustrated in FIG. 5 where the reverse operations of those inFIG. 4 are performed. In FIG. 5, an antenna receives the Radio-Frequency(RF) analog signal and after passing further processing units (such asfilters, amplifiers, frequency down-converters, and analog-to-digitalconverters) the resulting digital received signal 510 passes through atime windowing unit 520 and the CP is removed 530. Subsequently, the CSof the transmitted CAZAC-based sequence is restored 540, a Fast FourierTransform (FFT) 550 is applied, the selection 560 of the transmitted REs565 is performed, and correlation 570 with the CAZAC-based sequencereplica 580 is applied. The resulting output 590 can then be passed to achannel estimation unit, such as a time-frequency interpolator.

In addition to the DMRS transmission, the transmission from a UE ofcontrol signals or RS in the PUCCH and their reception by the NodeB mayalso be based on CAZAC sequences and be respectively performed aspreviously described.

Different CSs of a CAZAC sequence provide orthogonal sequences.Therefore, for a given CAZAC sequence, different CSs can be allocated todifferent UEs and achieve orthogonal DMRS multiplexing in the same RBs.This principle is illustrated in FIG. 6. In order for the multiple CAZACsequences 610, 630, 650, and 670 generated from multiple correspondingCSs 620, 640, 660, and 680 of the same CAZAC sequence to be orthogonal,the CS value 690 should exceed the channel propagation delay spread D(including a time uncertainty error and filter spillover effects). IfT_(S) is the duration of one sub-frame symbol, the number of CSs isequal to └T_(s)/D┘ where └ ┘ denotes the “floor” operation which roundsa number down to its lower integer.

For a PUSCH transmission associated with an UL SA, the UL SA is assumedto include a Cyclic Shift Indicator (CSI) indicating the CS for theCAZAC sequence used as DMRS. For SPS PUSCH transmissions, the NodeB alsoprovides, through higher layer signaling, to the UE the CSI value. Table1 shows a mapping of CSI values to CS values.

TABLE 1 Mapping of CSI Values to CS Values. CSI Value CS Value 000 CS₀ =0 001 CS₁ = 6 010 CS₂ = 3 011 CS₃ = 4 100 CS₄ = 2 101 CS₅ = 8 110 CS₆ =10 111 CS₇ = 9

CAZAC-based sequences of the same length typically have lowcross-correlations, which is important for minimizing mutualinterference. CAZAC-based sequences of different lengths have a widedistribution of cross-correlation values and large values often occur.FIG. 7 shows the Cumulative Density Function (CDF) of cross-correlationvalues for length-12 CAZAC-based sequences resulting from cyclicallyextending a length-11 Zadoff-Chu (ZC) sequence, truncating a length-13ZC sequence, or computer generation of length-12 CAZAC sequences.Variations in cross-correlation values are observed and even largercross-correlation values may occur between CAZAC-based sequences ofdifferent lengths. Randomization of the occurrence of largecross-correlations can be achieved by sequence hopping where thesequence is selected from a predetermined set of sequences according toa hopping pattern such, as for example, a pseudo-random pattern havingthe slot number as one of its arguments.

Sequence hopping is among CAZAC-based sequences of the same length thatbelong either to the same group or to different groups. A group ofCAZAC-based sequences consists of sequences with different lengths, eachcorresponding to each of the possible PUSCH RB allocations. For example,if 30 CAZAC-based sequences exist for the minimum allocation of 1 RB andsince the number of available CAZAC-based sequences increases as thenumber of RBs increases, 30 sequence groups can always be generated. Forlarge RB allocations, such as at least 6 RBs, 2 sequences can beincluded in each group of CAZAC-based sequences. Sequence hopping amongsequences in different groups will be referred to as group sequencehopping while sequence hopping among sequences in the same group (forallocations of at least 6 RBs) will just be referred to as sequencehopping. Group sequence hopping and sequence hopping (within the samesequence group) are respectively enabled or disabled by the NodeB forall UEs in its cell and for all applicable signals using transmission ofsequences (DMRS in the PUSCH or control signals and RS in the PUCCH)through broadcast signaling of the respective (cell-specific)parameters: Group-hopping-enabled and Sequence-hopping-enabled.

Multi-User Multiple-Input Multiple-Output (MU-MIMO) can improve thespectral efficiency of a communication system. With MU-MIMO, PUSCHtransmissions from multiple UEs share at least part of a BW. MU-MIMO isfacilitated if the NodeB can obtain interference-free estimates of thechannel medium the MU-MIMO UEs experience. This requires orthogonalreception for the respective DMRS. If the PUSCH transmissions fromMU-MIMO UEs share exactly the same BW, orthogonal DMRS multiplexing canbe obtained using different CS of the same CAZAC sequence. However, ifthe PUSCH transmissions from MU-MIMO UEs do not share exactly the sameBW, orthogonal DMRS multiplexing using different CS is not possiblebecause the respective CAZAC-based sequences have different lengths.Orthogonal Covering Codes (OCC) can then be used to provide orthogonalDMRS multiplexing in the time domain. For the sub-frame structure inFIG. 1 which has 2 DMRS symbols, the OCCs can be {1, 1} and {1, −1}.Regarding the CS, the OCC should also be indicated for the DMRStransmission in the PUSCH.

Two classes of UEs are assumed to coexist in the communication system.The first class of UEs, referred to as legacy-UEs, do not support OCCand rely only on the CS for orthogonal DMRS multiplexing. The secondclass of UEs, referred to as Advanced-UEs, support OCC and can rely onboth OCC and CS for orthogonal DMRS multiplexing.

A required restriction for the application of OCC is the absence ofsequence hopping Because of the sub-frame structure in FIG. 1,time-domain orthogonality is not possible if the DMRS transmission ineach sub-frame slot uses a different CAZAC sequence. Therefore, althoughOCC is only needed by Advanced-UEs for MU-MIMO transmissions overdifferent BWs, the performance of all UEs is degraded by the requirementto disable sequence hopping over the entire cell. Moreover, as sequenceplanning to achieve low cross-correlations is typically impractical,PUCCH transmissions, which are assumed to rely entirely on CAZACsequences, and occur over only one RB are particularly impacted which ishighly undesirable given that control information has enhancedreliability requirements.

Therefore, there is a need to define a mapping of CSI values to OCC andCS values that optimizes DMRS multiplexing among Advanced-UEs and amonglegacy-UEs and Advanced-UEs.

There is also need to enable sequence hopping in a cell while supportingtime-domain orthogonality through the application of OCC for the DMRStransmission in the PUSCH.

Finally, there is need to separate the application of sequence hoppingbetween sequences used in PUSCH transmissions and sequences used inPUCCH transmissions.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve at leastthe aforementioned problems in the prior art and the present inventionprovides methods and an apparatus to support the configuration of theDMRS transmission parameters, through the application of a CS and anOCC, to disable sequence hopping for the DMRS in PUSCH transmissionsfrom a UE when sequence hopping is enabled in the cell, and to separatethe application of sequence hopping between PUSCH and the PUCCH.

In accordance with an aspect of the present invention, a method of a UEis provided for transmitting a reference signal. The method includesreceiving a first parameter, which is a cell specific parameter;receiving a second parameter, which is a UE specific parameter;receiving a cyclic shift indicator (CSI) indicating a cyclic shift for asequence and an orthogonal covering code; acquiring the reference signalfor a PUSCH, based on the CSI and the second parameter; and transmittingthe reference signal on the PUSCH. Group sequence hopping is not appliedto acquire the reference signal, if the first parameter indicates thatthe group sequence hopping is enabled and the second parameter indicatesthat the group sequence hopping is disabled. The first parameterincludes a group hopping enabled parameter, and the group sequencehopping includes hopping among different groups.

In accordance with another aspect of the present invention, a method ofa base station is provided for receiving a reference signal. The methodincludes transmitting a first parameter, which is a cell specificparameter; transmitting a second parameter, which is a UE specificparameter; transmitting a cyclic shift indicator (CSI) indicating acyclic shift for a sequence and an orthogonal covering code; andreceiving the reference signal, which is generated based on the CSI, ona PUSCH. The reference signal is generated by not applying groupsequence hopping, if the first parameter indicates that the groupsequence hopping is enabled and the second parameter indicates that thegroup sequence hopping is disabled. The first parameter includes a grouphopping enabled parameter, and the group sequence hopping includeshopping among different groups.

In accordance with another aspect of the present invention, a UE isprovided for transmitting a reference signal. The UE includes atransceiver configured to transmit and receive signals; and a controllerconfigured to control the transceiver to receive a first parameter,which is a cell specific parameter, to control the transceiver toreceive a second parameter, which is a UE specific parameter, to controlthe transceiver to receive a cyclic shift indicator (CSI) indicating acyclic shift for a sequence and an orthogonal covering code, to controlto acquire the reference signal for a PUSCH, based on the CSI and thesecond parameter, and to control the transceiver to transmit thereference signal on the PUSCH. Group sequence hopping is not applied toacquire the reference signal, if the first parameter indicates that thegroup sequence hopping is enabled and the second parameter indicatesthat the group sequence hopping is disabled. The first parameterincludes a group hopping enabled parameter, and the group sequencehopping includes hopping among different groups.

In accordance with another aspect of the present invention, a basestation is provided for receiving a reference signal. The base stationincludes a transceiver configured to transmit and receive signals; and acontroller configured to control the transceiver to transmit a firstparameter, which is a cell specific parameter, transmit a secondparameter, which is a UE specific parameter, transmit a cyclic shiftindicator (CSI) indicating a cyclic shift for a sequence and anorthogonal covering code, and receive the reference signal, which isgenerated based on the CSI, on a PUSCH. The reference signal isgenerated by not applying group sequence hopping, if the first parameterindicates that the group sequence hopping is enabled and the secondparameter indicates that the group sequence hopping is disabled. Thefirst parameter includes a group hopping enabled parameter, and thegroup sequence hopping includes hopping among different groups.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a UL sub-frame structure for PUSCHtransmission in the UL of the communication system;

FIG. 2 is a block diagram illustrating the coding process of a SA in theNodeB;

FIG. 3 is a block diagram illustrating the decoding process of a SA inthe UE;

FIG. 4 is a block diagram illustrating a transmitter structure for aCAZAC-based sequence;

FIG. 5 is a block diagram illustrating a receiver structure for aCAZAC-based sequence;

FIG. 6 is a diagram illustrating the orthogonal RS multiplexing usingdifferent cyclic shifts of a CAZAC sequence;

FIG. 7 is a diagram illustrating the Cumulative Density Function (CDF)of cross-correlation values for length-12 CAZAC-based sequences;

FIG. 8 is a diagram illustrating the interpretation of the mapping ofCSI values to CS and OCC values depending on the use of group sequencehopping or sequence hopping within a group;

FIG. 9 is a diagram illustrating the application of sequence hoppingdepending on the “OCC-enabled” parameter value the NodeB informs the UEthrough RRC signaling; and

FIG. 10 is a diagram illustrating the different applicability ofsequence hopping in the PUSCH and in the PUCCH depending on the“OCC-enabled” parameter and the cell-specific enabling of sequencehopping.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete and willfully convey the scope of the invention to those skilled in the art.

Additionally, although the present invention is described in relation toa Single-Carrier Frequency Division Multiple Access (SC-FDMA)communication system, it also applies to all Frequency DivisionMultiplexing (FDM) systems in general and to an Orthogonal FrequencyDivision Multiple Access (OFDMA), OFDM, FDMA, Discrete Fourier Transform(DFT)-spread OFDM, DFT-spread OFDMA, SC-OFDMA, and SC-OFDM system inparticular.

The following two goals are considered:

a) Defining a mapping of CSI values to CS and OCC values, whichoptimizes DMRS multiplexing among Advanced-UEs and among legacy-UEs andAdvanced-UEs.

b) Enabling sequence hopping in the PUSCH in conjunction with theapplication of OCC.

The first goal considers that the CSI value provides signaling supportfor orthogonal DMRS multiplexing among UEs also in the time domain byindicating a respective OCC value in addition to a CS value. Theconventional CSI Information Element (IE) remains unchanged and noadditional bits are introduced in the CSI IE to indicate that the OCC isbeing applied to the DMRS. Instead, the CSI value provides mapping toboth the CS and the OCC values.

The CSI IE is assumed to consist of 3 bits and address a CS from a setof eight CS, {CS₀, CS₁, CS₂, CS₃, CS₄, CS₅, CS₆, and CS₇}. For example,for a CAZAC-based sequence r(n) in the frequency domain, where n is theRE index, the DMRS sequence is r^((α))(n)=e^(jαn) r(n) where α is the CSgiven as α=2πn_(CS)/12 where n_(CS)=(N_(DMRS)+n_(DMRS))mod12 andN_(DMRS) is a cell-specific values that is common to all UEs in a celland n_(DMRS) is determined from the CSI.

For legacy-UEs, the mapping in Table 1, and the goal of selecting CSvalues with the largest mutual distance in the time domain (modulo 12),the optimal CS values for various numbers of MU-MIMO legacy-UEs are:

a) 2 MU-MIMO legacy-UEs: CS₀ and CS₁

b) 3 MU-MIMO legacy-UEs: CS₀, CS₃ and CS₅

c) 4 MU-MIMO legacy-UEs: CS₀, CS₁, CS₂ and CS₇.

For more than 4 MU-MIMO legacy-UEs, the optimal CS values practicallyconsist of the first 4 ones, CS0, CS1, CS2 and CS7, and any otheradditional values. Legacy-UEs are assumed to not support OCC for theirDMRS transmission and therefore they have the implicit assignment of OCC{1, 1}. Since the communication system is assumed to support bothlegacy-UEs and Advanced-UEs, the OCC {1, 1} will be implicitly used bylegacy-UEs and will not be as readily available to Advanced-UEs as theOCC {1, −1}. Rules for the CSI to OCC/CS mapping for Advanced-UEs willnow be considered.

The first rule is that the CSI values indicating OCC {1, 1} shouldindicate different CS values for Advanced-UEs than for legacy-UEs inorder to maximize MU-MIMO capacity among legacy-UEs and Advanced-UEs.

The second rule is that an equal number of CSs is associated with OCC{1, 1} and with OCC {1, −1}. For a CSI consisting of 3 bits indicating atotal of 8 CS/OCC combinations, this implies that 4 CS values areassociated with OCC {1, 1} and 4 CS values are associated with OCC {1,−1}.

The third rule is that different CSs associate with OCC {1, 1} and withOCC {1, −1}. Then, DMRS orthogonal multiplexing is achieved both throughOCC and through CS, which enhances its robustness against temporalchannel variations or large channel propagation delays.

The fourth rule is that CS values associated with OCC {1, 1} havemaximum mutual distance and CS values associated with OCC {1, −1} alsohave maximum mutual distance.

The above rules also allow the NodeB to arbitrarily select any CSI valuewhile ensuring a robust mapping of the CSI values to CS and OCC values.This is important because the CSI may also be used to indicate theresource for the corresponding HARQ-ACK signal transmission from theNodeB (in response to the reception by the NodeB of the PUSCHtransmission by the UE in case it is scheduled by the UL SA containingthe CSI).

Table 2 shows the mapping of the CSI values to the CS and OCC valuesused for the DMRS transmission by Advanced-UEs in accordance with thepreviously described rules.

TABLE 2 First Mapping of CSI Values to CS and OCC Values - Advanced-UEs.CSI Value CS Value OCC Value 000 2 {1, −1} 001 8 {1, −1} 010 5 {1, −1}011 1 {1, 1} 100 7 {1, 1} 101 4 {1, 1} 110 10 {1, 1} 111 11 {1, −1}

The mapping in Table 3 also satisfies the CSI to CS-and-OCC mappingrules. Relative to the mapping in Table 2, the only difference is thatthe association between CS values and OCC values is reversed.

TABLE 3 Second Mapping of CSI Value to CS and OCC Values - Advanced-UEs.CSI Value CS Value OCC Value 000 1 {1, −1} 001 7 {1, −1} 010 4 {1, −1}011 2 {1, 1} 100 8 {1, 1} 101 5 {1, 1} 110 11 {1, 1} 111 10 {1, −1}

In principle, the association of a specific CSI value with a pair of CSand OCC values can be arbitrary and not confined to ones in Table 2 orTable 3. For example, an alternative association may be used such asTable 4 or Table 5 below. This is because the previously described rulesconsider only the association between CS and OCC values for Advanced-UEsand their relation to the CS values for legacy-UEs. In this respect, theCSI value associated with a CS/OCC pair is immaterial. Nevertheless, theassociation of a CSI value with a pair of CS and OCC values in Table 2or Table 3 is beneficial.

TABLE 4 Third Mapping of CSI Value to CS and OCC Values - Advanced-UEs.CSI Value CS Value OCC Value 000 2 {1, −1} 001 8 {1, −1} 010 5 {1, −1}011 11 {1, −1} 100 1 {1, 1} 101 7 {1, 1} 110 4 {1, 1} 111 10 {1, 1}

TABLE 5 Fourth Mapping of CSI Value to CS and OCC Values - Advanced-UEs.CSI Value CS Value OCC Value 000 5 {1, −1} 001 11 {1, −1} 010 8 {1, −1}011 1 {1, 1} 100 7 {1, 1} 101 4 {1, 1} 110 10 {1, 1} 111 2 {1, −1}

The second goal considers enabling DMRS sequence hopping in conjunctionwith the application of OCC in the PUSCH. DMRS sequence hopping needs tobe disabled in case of MU-MIMO among UEs having PUSCH transmission withdifferent bandwidths in order to allow for orthogonal DMRS multiplexingrelying on different OCCs.

Since the Node B can control whether sequence hopping (either acrossgroups of sequences or within a group of sequences) is applied to itscell and can control whether MU-MIMO transmissions are over differentPUSCH bandwidths, it can select between these two features (sequencehopping or MU-MIMO over different PUSCH bandwidths). If the(cell-specific) “group-hopping-enabled” and the“sequence-hopping-enabled” parameters indicate that sequence hopping isdisabled in the cell served by the NodeB, the mapping of CSI values toOCC/CS values can be, for example, as in Table 2, Table 3, Table 4, orTable 5. If the “group-hopping-enabled” or the“sequence-hopping-enabled” parameter indicates that sequence hopping isenabled in the cell, the CSI mapping to CS values for Advanced-UEs canbe as in Table 1.

FIG. 8 illustrates the interpretation by an Advanced-UE of the mappingfrom the CSI values to CS and OCC values. If the NodeB indicates 810that either group sequence hopping or sequence hopping within a group isenabled 820, an Advanced-UE assumes that the CSI indicates only CSvalues 830, for example using the mapping in Table 1. Otherwise 840, anAdvanced-UE assumes that the CSI indicates both CS and OCC values 850,for example using the mapping in Table 2.

Alternatively, a new (UE-specific) parameter “OCC-enabled” can bedefined for Advanced-UEs in order to separate the application ofsequence hopping among legacy-UEs and Advanced-UEs. The “OCC-enabled”parameter is signaled through RRC to the Advanced-UE and indicateswhether sequence hopping is enabled or not (and may also interpret theCSI as mapping to both CS and OCC values or as mapping only to CSvalues) when the NodeB already indicates (through cell-specificsignaling) that sequence hopping is enabled in its cell. In the firstcase, the Advanced-UE follows the indication of the“group-hopping-enabled” and “sequence-hopping-enabled” parameters by theNodeB regarding sequence hopping. In the second case, the Advanced-UEdisables both group sequence hopping and sequence hopping within a groupeven when the (cell-specific) “group-hopping-enabled” and“sequence-hopping-enabled” parameters indicate that sequence hopping isenabled.

FIG. 9 illustrates the mapping of CSI values to CS and OCC values andthe application of sequence hopping by an Advanced-UE depending on thevalue of the “OCC-enabled” parameter signaled by the NodeB. AnAdvanced-UE evaluates whether “OCC-enabled=Enabled” 910 and if the NodeBindicates that it is enabled 920 (implying sequence hopping isdisabled), the Advanced-UE may assume that the CSI value indicates botha CS value and an OCC value 930, using, for example, the mapping inTable 2, and the Advanced-UE does not apply sequence hopping to its DMRStransmission regardless of the respective (cell-specific) NodeBindication for sequence hopping. Otherwise, if OCC-Enabled is notenabled 940, the Advanced-UE may assume that the CSI value indicatesonly CS values, using, for example, the mapping in Table 1, and followsthe (cell-specific) NodeB indication regarding sequence hopping for itsDMRS transmission 950.

Since signal transmissions in the PUCCH are assumed to occur in one RB,only group sequence hopping can apply for the respective CAZAC-basedsequences (which, in addition to DMRS, may include HARQ-ACK signals orCQI signals). As the restrictions regarding sequence hopping from theintroduction of OCC do not occur in the PUCCH, an Advanced-UE is assumedto always follow the (cell-specific) indication of the“group-hopping-enabled” parameter by the NodeB regardless of the(UE-specific) indication for sequence hopping and application of OCC forthe DMRS transmission in the PUSCH (through the UE-specific“OCC-enabled” parameter).

FIG. 10 illustrates the different applicability of the cell-specific“group-hopping-enabled” parameter for CAZAC-based sequence hopping inthe PUSCH and in the PUCCH depending on the “OCC-enabled” parameter. Ifthe “group-hopping-enabled” parameter 1010 indicates that group hoppingfor CAZAC-based sequence is not enabled 1020, group sequence hopping ofCAZAC-based sequences does not apply either in the PUSCH or in the PUCCH1030. If the “group-hopping-enabled” parameter indicates that grouphopping for CAZAC-based sequence is enabled 1040, then group hopping ofCAZAC-based sequences in the PUSCH depends on the “OCC-enabled”parameter 1050. If the “OCC-enabled” parameter is not set 1060, groupsequence hopping of CAZAC-based sequences applies to both PUSCH andPUCCH 1070. If the “OCC-enabled” parameter is set 1080, group sequencehopping of CAZAC-based sequences applies only to PUCCH 1090.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method of a user equipment (UE) fortransmitting a reference signal, the method comprising: receiving afirst parameter, which is a cell specific parameter, via higher layersignaling; receiving a second parameter, which is a UE specificparameter, via the higher layer signaling; receiving a cyclic shiftindicator (CSI) indicating a cyclic shift for a sequence and anorthogonal covering code on a physical downlink control channel (PDCCH);acquiring the reference signal for a physical uplink shared channel(PUSCH), based on the CSI and the second parameter; and transmitting thereference signal on the PUSCH, wherein group sequence hopping is notapplied to acquire the reference signal, for orthogonal reference signalmultiplexing, if the first parameter indicates that the group sequencehopping is enabled and the second parameter indicates that the groupsequence hopping is disabled, wherein the first parameter includes agroup hopping enabled parameter, and wherein the group sequence hoppingincludes hopping among different groups.
 2. The method of claim 1,wherein the reference signal is a demodulation reference signal used fordemodulation of uplink data.
 3. The method of claim 1, wherein thesecond parameter includes an orthogonal covering codes (OCC)-enabledparameter that indicates that the group sequence hopping is disabled. 4.A method of a base station for receiving a reference signal, the methodcomprising: transmitting a first parameter, which is a cell specificparameter, via higher layer signaling; transmitting a second parameter,which is a user equipment (UE) specific parameter, via the higher layersignaling; transmitting a cyclic shift indicator (CSI) indicating acyclic shift for a sequence and an orthogonal covering code on aphysical downlink control channel (PDCCH); and receiving the referencesignal, which is generated based on the CSI, on a physical uplink sharedchannel (PUSCH), wherein the reference signal is generated by notapplying group sequence hopping, for orthogonal reference signalmultiplexing, if the first parameter indicates that the group sequencehopping is enabled and the second parameter indicates that the groupsequence hopping is disabled, wherein the first parameter includes agroup hopping enabled parameter, and wherein the group sequence hoppingincludes hopping among different groups.
 5. The method of claim 4,wherein the reference signal is a demodulation reference signal used fordemodulation of uplink data.
 6. The method of claim 4, wherein thesecond parameter includes an orthogonal covering codes (OCC)-enabledparameter that indicates that the group sequence hopping is disabled. 7.A user equipment (UE) for transmitting a reference signal, the UEcomprising: a transceiver configured to transmit and receive signals;and a controller configured to control the transceiver to receive afirst parameter, which is a cell specific parameter, via higher layersignaling, to control the transceiver to receive a second parameter,which is a UE specific parameter, via the higher layer signaling, tocontrol the transceiver to receive a cyclic shift indicator (CSI)indicating a cyclic shift for a sequence and an orthogonal covering codeon a physical downlink control channel (PDCCH), to control to acquirethe reference signal for a physical uplink shared channel (PUSCH), basedon the CSI and the second parameter, and to control the transceiver totransmit the reference signal on the PUSCH, wherein group sequencehopping is not applied to acquire the reference signal, for orthogonalreference signal multiplexing, if the first parameter indicates that thegroup sequence hopping is enabled and the second parameter indicatesthat the group sequence hopping is disabled, wherein the first parameterincludes a group hopping enabled parameter, and wherein the groupsequence hopping includes hopping among different groups.
 8. The UE ofclaim 7, wherein the reference signal is a demodulation reference signalused for demodulation of uplink data.
 9. The UE of claim 7, wherein thesecond parameter includes an orthogonal covering codes (OCC)-enabledparameter that indicates that the group sequence hopping is disabled.10. A base station for receiving a reference signal, the base stationcomprising: a transceiver configured to transmit and receive signals;and a controller configured to control the transceiver to transmit afirst parameter, which is a cell specific parameter, via higher layersignaling, transmit a second parameter, which is a user equipment (UE)specific parameter, via the higher layer signaling, transmit a cyclicshift indicator (CSI) indicating a cyclic shift for a sequence and anorthogonal covering code on a physical downlink control channel (PDCCH),and receive the reference signal, which is generated based on the CSI,on a physical uplink shared channel (PUSCH), wherein the referencesignal is generated by not applying group sequence hopping, fororthogonal reference signal multiplexing, if the first parameterindicates that the group sequence hopping is enabled and the secondparameter indicates that the group sequence hopping is disabled, whereinthe first parameter includes a group hopping enabled parameter, andwherein the group sequence hopping includes hopping among differentgroups.
 11. The base station of claim 10, wherein the reference signalis a demodulation reference signal used for demodulation of uplink data.12. The base station of claim 10, wherein the second parameter includesan orthogonal covering codes (OCC)-enabled parameter that indicates thatthe group sequence hopping is disabled.